This week’s question is one many people ask this time of year, especially during the recent heat wave when they will be trying to cool off on and in the water: “How can you tell where in the bay sea nettles will be this summer?”

Sea nettles (Chrysaora quinquecirrha) are the most abundant jellyfish in the Chesapeake Bay and its tidal tributaries. These whitish-colored jellies soar in numbers in summer and can be a pesky (and painful) nuisance to swimmers. But thankfully, scientists can predict when and where sea nettles will be present in the Chesapeake Bay based on environmental conditions.

Scientists use a computer model to predict the probability of encountering these stinging jellies in your local river or favorite Bay swimming hole. The computer model compares salinity, water temperature and sea nettle density data from the spring, summer and fall of 1987-2000.

Based on this data, scientists found that sea nettles prefer water temperatures ranging from 78.8 - 86 degrees Fahrenheit and a salinity of 10-16 PSU (practical salinity units). For comparison, seawater has an average PSU of 35 and tidal fresh water has a PSU of less than .5. So when conditions in the Bay are within these temperature and salinity ranges, you will likely encounter sea nettles.

NOAA has created a sea nettle presence probability map that displays the likelihood of encountering sea nettles throughout the Bay and its rivers.This is your best resource to beat the sting and see if sea nettles are present in your area.

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